Stiffening assembly for a fuel tank

ABSTRACT

A tank assembly and a stiffening assembly include first and second inserts and an elongate coupler. The inserts comprise a base having flange, a head, and a neck. The elongate body has first and second couplers at respective first and second ends of the body, each coupler including a pocket sized to receive the head of a respective one of the inserts. The related method include forming a fuel tank such that the tank wall carries at least a first and second insert, locating a rigid connector within the tank interior aligned with the first and second inserts, the connector including a first coupler and a second coupler, and coupling at least a portion of the first insert with the first coupler and at least a portion of the second insert with the second coupler to limit movement of the two wall portions relative to each other.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application Ser. No. 62/106,404 filed on Jan. 22, 2015, entitled “STIFFENING ASSEMBLY FOR A FUEL TANK,” the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a structure supporting a fuel tank under pressure.

BACKGROUND

Fuel tanks for automotive vehicles have been made from metal and plastic materials. Fuel tanks are formed in various sizes and shapes as required for the various applications in which they are used. Fuel tanks used in passenger vehicles must meet certain requirements relating to, for example, resistance to rupture upon impact and permeability to hydrocarbons in fuel vapor. Typical plastic fuel tanks include a single wall of material and that wall may be formed from a single material or multiple layers of different materials. Particularly in fuel tanks, there is a need to make containers having more than one wall or layer of different materials in order to meet various requirements, for example with respect to mechanical stability and resistance to higher pressures in modern systems. Up to now the making of such containers requires complex multi-step manufacturing methods.

SUMMARY

The present disclosure provides a stiffening assembly for a fuel tank. The stiffening assembly includes first and second inserts for the wall of a fuel tank, and an elongate coupler. The inserts each comprise a base having flange, a head, and a neck coupling the base to the head. The neck may have a portion that is narrower than at least a portion of the head. The elongate body has first and second couplers at respective first and second ends of the body, each coupler including a pocket sized to receive the head of a respective one of the inserts.

According to more detailed aspects, each insert may be integrally formed in one piece. The heads of the inserts may include voids at their distal ends. The inserts may be partially hollow, and may include a cavity opening at the base. The inserts may include ribs projecting into the cavity. The couplers can be separately formed and attached to the elongate body, the couplers and body including corresponding tabs and detents for attachment. The elongate body may define first and second openings at the first and second ends, the first and second openings receiving the first and second couplers. The pockets may be defined by a plurality of fingers, the plurality of fingers being moveable between a first state and a second state, the plurality of fingers moving radially inwardly from the first state to the second state. The first and second openings are sized to cause the plurality of fingers to move to the second state as the fingers are received within the openings. The elongate member may include two tubular members defining the first and second ends and at least a third end, wherein the stiffening assembly further comprises a third insert and a third coupler at the third end.

A fuel tank assembly according to the present disclosure includes a fuel tank having a wall defining a tank interior, and a stiffening assembly as described herein. A first exterior portion of the tank wall carries the first insert and a second exterior portion of the wall carries the second insert, and wherein the body and couplers are received within the tank interior. Here, the wall may be interposed between the inserts and the couplers.

The present disclosure also provides a method of manufacturing a fuel tank. The method may include the steps of forming a fuel tank, wherein the tank carries at least a first and second insert, locating a rigid connector within the tank interior, aligned with the first and second inserts, the connector including a first coupler and a second coupler, and coupling at least a portion of the first insert with the first coupler and at least a portion of the second insert with the second coupler. The connector spans between two spaced apart wall portions of the tank to limit movement of the two wall portions relative to each other.

According to more detailed aspects, the forming step may further comprise overmolding the insert while the fuel tank is in a parison form. The forming step may also further comprise shaping a tank wall carrying the insert so that the insert defines a projection that extends at least partially radially inwardly into a tank interior. In one form, the fuel tank is formed in a mold having portions moveable between open and closed positions, and the step of coupling the insert with the first coupler is accomplished by movement of the mold portions toward their closed position. The interior of the parison may be accessed during the tank forming process to allow insertion of the connector into the parison interior, e.g. by cutting or tearing the parison into two portions. The method may also include the step of coupling the first and second couplers to the connector. The first coupler may be coupled to the connector simultaneously with coupling the first coupler to the first insert.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred embodiments and best mode will be set forth with reference to the accompanying drawings, in which:

FIG. 1 is an exploded view of a portion of a fuel tank and a stiffening assembly within the fuel tank;

FIG. 2 is a perspective view of the stiffening assembly of FIG. 1 in a partially assembled state;

FIG. 3 is a perspective view of the stiffening assembly of FIG. 1 in a fully assembled state;

FIGS. 4A-4C illustrate additional embodiments of the stiffening assembly; and

FIG. 5 is a partial, cross-sectional view of a portion of the stiffening assembly and part of a fuel tank wall along section lines 5-5 of FIG. 3.

DETAILED DESCRIPTION

Referring in more detail to the drawings, FIG. 1 illustrates a portion of a fuel tank 10 (in a parison form) and a stiffening assembly 12 coupling two portions 14, 16 of a fuel tank wall 18. The stiffening assembly 12 provides structural support for the fuel tank 10 and minimizes deformation of the shape of the fuel tank (e.g., due to temperature changes, pressure changes, or both).

The fuel tank wall 18 defines an enclosed volume or interior 20 for carrying liquid fuel. The wall 18 may have any suitable thickness; further, the thickness of the wall may vary depending on the location in the tank 10. And the tank may be comprised of any suitable material, such as (but not limited to) a multi-layer plastic construction having one or more structural layers, one or more adhesive layers, and one or more vapor barrier layers.

The stiffening assembly 12 comprises two or more inserts 30 and a connecting assembly 32. As will be explained below, the inserts 30 are carried by the fuel tank wall 18, and the connecting assembly 32 spans between and couples one insert to the other thereby stiffening or supporting two connected or adjoined regions or portions 14, 16 of the fuel tank wall.

The inserts 30 may be identical; therefore, only one will be described below. The insert 30 has a base 36, a reduced diameter neck 38 axially extending from the base, and a head 42 extending from the neck. The illustrated base has a generally annular shape and is partially defined by a radially outwardly extending flange 46. In one embodiment, the periphery of the flange 46 is circular; however, the base 36 and/or flange 46 may have different shapes as desired. In at least some implementations, at least a portion of the flange 46 is radially wider than a portion of the neck 38.

The neck 38 may radially narrow as it extends axially from the base 36, providing a generally conical or frustoconical shape. Or as in the illustrated embodiment, the neck may be curved between the base and head providing a partially hyperbolic shape. In some implementations, at least a portion of the neck 38 is radially narrower than a portion of the head 42. The neck 38 may be circumferentially continuous, if desired, or it may have recesses or other voids formed in it to improve connection of the tank to the insert 30.

The head 42 is connected to the neck 38 extending axially away therefrom, and at least a portion of the head 42 may be radially wider than at least a portion of the neck 38 adjacent to the head. In the implementation shown, the head is generally spherical; however again, this is merely an example. Other shapes are possible. The head 42 may have one or more voids 52 at a distal end 54. The voids 52 may be cavities or blind holes, through holes, or any combination thereof. For example, the cross-section shown in FIG. 5 illustrates the voids 52 as blind holes.

The base 36, neck 38, and head 42 of the insert may be integrally formed in one piece of material, such as by molding (e.g., a unibody construction). In at least one implementation, the insert 30 is formed of a polymeric, composite, or metal material.

The insert 30 may be at least partially hollow—having a cavity 56 opening at one side 41 of the base and extending towards the head 42 (see also FIG. 5). As will be described in greater detail below, the cavity 56 may be used to carry the insert 30 in a manufacturing mold so that the insert may be incorporated into a parison of the fuel tank 10. The cavity may be any suitable shape; and in some implementations, the insert 30 may not have a cavity.

FIG. 5 further illustrates that the insert 30 may have one or more ribs 58 that extend inwardly and define part of the cavity 56. To reinforce the strength of the insert 30, the ribs 58 may extend at least partially circumferentially and/or at least partially from the base 36 towards the head 42.

The insert 30 may include cavities or other voids, including openings therethrough, in one or more of the base 36, neck 38, and head 42 to facilitate connection of the insert to the fuel tank wall 18. For example, according to one embodiment shown in FIG. 5, the insert may comprise one or more circumferentially-spaced through holes 50 on the base 36 to further facilitate bonding of the insert to the parison fuel tank during manufacturing. Other embodiments do not comprise holes 50. The insert 30 is adapted to cooperate with the connecting assembly 32 to interconnect spaced apart portions 14, 16 of the fuel tank wall.

-   -   Returning to FIG. 1, the connecting assembly 32 includes a         cylindrical, tubular body 64 extending from a first end 66 to a         second end 68 and two couplers 62. Each end 66, 68 may have an         opening 70 a, 70 b extending from the respective end axially         inwardly. In the illustrated embodiment, the body 64 is hollow         and the openings 70 a, 70 b are in communication with one         another; however, this is not required. One or more         circumferentially spaced detent elements 76 may be provided in         the body 64 at or adjacent to the first end 66 and one or more         similar detent elements may be provided at or adjacent to the         second end 68. For example, in the illustrated embodiment, six         circumferentially spaced detent elements 76 are shown at each         end. The detent elements 76 are shown as circular through-holes;         however, this is merely an example and other implementations are         possible—e.g., the elements 76 need not be circular nor need the         elements pass entirely through the support body 64 (e.g., the         element 76 may be a cavity or depression extending radially         outwardly from an inner surface 78 of the body 64. Or for         example, the detent elements could be inwardly extending         protrusions adapted to couple to openings or cavities on the         couplers 62.

In FIG. 1, the body 64 is straight; however, other implementations also exist (see FIGS. 4A, 4B, 4C having support bodies 64′, 64″, 64′″, respectively). For example, the support may be curved or angled. It may have a T-shape, a Y-shape, a cross-shape, an X-shape, etc. (e.g., having three or more openings and passages). These of course are examples, and other embodiments also exist.

-   -   As shown in FIGS. 1-3, in at least one embodiment, a separate         coupler 62 is coupled to each end 66, 68 of the body 64, and the         connectors at each end 66, 68 of the body may be identical, so         only one coupler 62 will be described in detail hereafter. The         coupler 62 comprises a collar 80, a first attachment portion 82         and a second attachment portion 84. The first attachment portion         82 is adapted to interconnect the coupler 62 and the fuel tank         12 while the second attachment portion 84 is adapted to         interconnect the coupler 62 to the body 64. The collar 80 is         sized to be received within the opening 70 a (or 70 b) by a         sliding or interference fit. The collar 80 is shown having an         annular, cylindrical shape, but of course, other shapes are also         possible.     -   In the illustrated embodiment, the first attachment portion 82         includes one or more fingers 86 attached at one end 90 to and         extending from the collar 80 to a free end 94 (six fingers are         shown, although any number may be used). The fingers may extend         generally axially from the collar and may be radially inclined         so that the free ends 94 extend radially outwardly relative to         the collar 80. The fingers 86 may also be flexible, or pivoted         relative to the collar 80, such as about a living hinge defined         at the fixed end 90, so that the free ends 94 may move radially         inwardly. Hence, the fingers 86 may have a first state where the         distance between the inner surfaces of the free ends of the         fingers is greater than in a second state of the fingers when at         least a portion of the fingers are flexed or moved inwardly. In         the implementation shown, the fingers 86 include a narrow         portion 88 at the fixed end 90 leading to a wider portion 92         that defines the free end 94. Each finger 86 may be provided in         or biased to a radially outwardly position and is flexible to         move inwardly when a sufficient force is applied to it. The six         fingers 86 may be evenly, circumferentially spaced around the         collar 80. The inner surface of each finger may be concave so         that the fingers collectively define a pocket 96 (see also FIG.         5). The pocket 96 is adapted to receive at least a portion of         the head 42 of the insert 30, as will be described later.     -   In the illustrated embodiment, the second attachment portion 84         includes multiple protrusions 100 also carried by and, in at         least some implementations, cantilevered from the collar 80 so         that they have a fixed end 102 and a free end 104 (six         protrusions are shown although any number may be used). The         protrusions may be evenly spaced around the collar and may be         alternated with the fingers 86, if desired. Of course, other         arrangements may be used as desired. Like the fingers 86, the         protrusions 100 may extend axially and radially outwardly from         their fixed ends 102 toward their free ends 104. In one         embodiment, the protrusions 100 terminate where the wider         portion 92 of the fingers 86 begin and a gap 106 is provided         surrounding the protrusions 100 so that the protrusions are         generally independent of the fingers. In at least one         embodiment, each protrusion 100 is provided in or biased to a         radially outwardly inclined position having at least a portion         that extends radially outwardly farther than the adjacent         portion of the fingers 86. Each protrusion 100 may be flexible         so that at least a portion is moveable or may be bent radially         inwardly; e.g., flexing at or near the collar 80, such as about         a living hinge provided between the collar 80 and protrusion         100. And each protrusion may be resilient to return radially         outwardly at least partially back to its unflexed position when         a force on the protrusion is sufficiently reduced or removed.

FIGS. 1-3 collectively illustrate at least a portion of a manufacturing process for a fuel tank. In one embodiment, the tank 10 and its wall 18 may be molded from a polymeric material in a mold having two halves that define a mold cavity that defines the outer shape of the fuel tank. In the fuel tank forming process, the mold halves may be opened and the inserts 30 may be positioned within the mold halves before the polymeric material is provided into the mold cavity. In at least some implementations, the inserts 30 are oriented with the base 36 and/or cavity 56 engaged with or carried by each mold half and the head 42 extending inwardly into the mold cavity. The inserts 30 may be provided in pairs, with a first insert carried by one mold half and a second insert carried by the other mold half and aligned with the first insert. Hence, when the mold halves are closed together to define the mold cavity, the inserts 30 are moved toward each other and remain aligned (in at least some implementations).

An extruded parison used to form the fuel tank may be provided into the mold, between the separated mold halves. Next, the mold halves may be at least partially closed and pressurized gas (e.g., air) may be provided into an interior of the parison using a blow pin to pre-blow the parison outwardly into the mold cavity. During the expansion, the head 42 and neck 38 of the inserts 30 may be covered with the parison material which conforms to their shape, and the base 36 may be at least partially embedded therein. Thus, the expansion may shape at least a portion of the tank wall 18 so that each of the inserts 30 define a projection that extends at least partially radially inwardly into the tank interior. These projections may be defined by the size and shape of the head 42, the neck 38, and/or even the base 36, as well as well as the thickness of the parison; thus, for example, the projections may have any desired diameter(s) (and varying diameters/shape), inwardly extending length, etc.

Thereafter, the parison material may separated into parison halves or portions, such as by cutting or tearing the parison, with one parison half in each mold half. The mold halves then may be opened to expose the interior of the parison halves. This provides access to the interior of the parison so that fuel tank components, such as the connecting assembly 32, may be located within the interior of the parison. One such method of forming a parison and separating a parison into parison halves in order to locate components therein is disclosed in U.S. patent application Ser. No. 12/491,964, the disclosure of which is incorporated by reference herein in its entirety.

-   -   With the mold opened, the connecting assembly 32 is introduced         between the mold halves and the parison halves. Here, the         couplers 62 are provided in an initial assembly position, as         shown in FIG. 2. In this initial position, the collars 80 are at         least partially received within the tube openings 70 a, 70 b,         optionally with the protrusions 100 received within the         respective opening, displaced inwardly and frictionally engaged         with the inner surface 78 of the tubular body 64. In this         initial assembly position, the connecting assembly 32 is         positioned between the mold halves with the pockets 96 defined         by the coupler fingers 86 being aligned with the heads 42 of the         inserts 30. The connecting assembly 32 may be held in this         position on an arm (e.g., a robot arm) or other actuator holding         the connecting assembly 32 until the couplers 62 initially         receive the heads 42 between the free ends 94 of the fingers 86,         and then the arm may be withdrawn from between the mold halves         so that the mold may be further and eventually, fully closed.     -   While the mold halves close, the heads 42 of the inserts 30 are         received within the pockets 96 of the couplers 62 and the free         ends 94 of the fingers 86 eventually engage the tank material         overlying the base 36. Further closing of the mold presses the         couplers 62 into the tubular body 64 simultaneously at each end         66, 68, and radially inwardly flexes the fingers 86 as the         fingers are increasingly received within the body 64. Upon full         closure of the mold, as shown in FIG. 3, the protrusions 100 are         aligned with the detent elements 76 and the protrusions 100         resiliently return radially outwardly to or toward their initial         state such that a portion of the protrusions 100 extends         outwardly into or through the detent elements 76. Also, the         fingers 86 are received within the body 64 sufficiently to         radially inwardly displace the fingers sufficiently so that the         fingers radially overlap the heads 42 of the inserts 30 so that         the heads are trapped within the pockets 96 defined in the         couplers 62. The components remain in this position as the         parison material is finally formed (e.g. final blow pressure is         applied within the parison interior). The material hardens and         the formed fuel tank 10 is removed from the mold.     -   In this position, outward movement of the fingers 86 is         prevented by the overlapping tubular body 64, and movement of         the body relative to the couplers 62 is prevented by engagement         of the protrusions 100 with the body 64 from within the detent         elements 76. In this way, the head 42 of each insert 30 remains         trapped in an associated pocket 96, and the fuel tank wall 18         portions remain interconnected. So connected, the portions 14,         16 of the fuel tank wall that are interconnected by the         connecting assembly 32 are inhibited or prevented from any         significant movement away from or toward each other. This is due         at least in part to the fuel tank wall 18 being securely trapped         between the respective heads 42 of the inserts 30 and the         couplers 62 such that forces tending to separate the fuel tank         walls are transferred to the tubular body 64 (via the inserts 30         and couplers 62) which may be rigid and substantially         inextensible.

Further, the stress on the tank 10 from such forces is experienced over a relatively large surface area at the interface between the insert base 36 and the tank wall 18 to prevent undue stress on any portion of the fuel tank. By increasing the surface area of the flange 46, the forces on the tank wall can be further dissipated, as desired for a particular application. By way of example, forces tending to separate the fuel tank walls 18 (e.g. expand the fuel tank outwardly) may occur due to increased pressure within the tank, or the weight of fuel in a full tank acting on the fuel tank wall. Further, temperature increases (both ambient temperature outside of the fuel tank 10 and the temperature within the fuel tank) can decrease the stiffness, rigidity, or strength of a polymeric fuel tank. Therefore, the fuel tank 10 with the stiffening assembly 12 may be used to contain fluid at increased pressures and/or with increased temperatures compared to tanks without such stiffening or connecting features. And, due to the increased stiffness and rigidity of the fuel tank provided by the stiffening assembly 12, a thinner fuel tank wall 18 can be used in applications compared to fuel tanks 10 without the assembly 12, which may lead to a cost savings and, in some instances, a weight savings.

-   -   The above described process is one example of a fuel tank         formation process. Other processes may be used to form a fuel         tank with the stiffening assembly 12 therein. For example, a         fuel tank may be formed from an uncut or undivided cylindrical         parison introduced between two open mold halves each carrying an         insert 30, similar to that described above. An arm may introduce         a carrier carrying the connecting assembly 32 through an open         end of the parison aligning the couplers 62 with the inserts 30.         The mold halves may be partially closed, an opposing end of the         parison may be at least partially closed using a gripper         mechanism, and pressurized air may be provided into the parison         to initially and partially expand it. The mold halves may be         partially closed until the couplers 62 at least partially         receive the heads 42 of the inserts 30, as described above.         Thereafter, the arm may be removed leaving the carrier and         connecting assembly 32 in place, and then, the mold halves may         be fully closed fully engaging the connecting assembly with the         inserts 30, having the parison trapped therebetween. During this         process, and even after the mold is fully closed, additional         pressurized air may be provided into the parison—e.g., to         maintain the parison open and prevent it from collapsing and to         form the parison into the desired fuel tank shape. Other aspects         of this method are disclosed in U.S. Pat. No. 6,712,234, the         disclosure of which is incorporated by reference herein in its         entirety.

In another assembly example, a fuel tank may be formed from sheets of material, such as in a vacuum forming or other type of process. With mold halves opened, material may be provided into both mold halves, overlapping the inserts 30. The material may then be formed into the cavities such as by vacuum forming. As described above, the connecting assembly 32 may be provided between the mold halves before they are closed so that the connecting assembly 32 is coupled to the inserts 30 as the mold halves close to form the fuel tank.

In another example, the connecting assembly 32 is provided into a fuel tank and coupled thereto after the tank is formed. In this embodiment, the tank is formed by overmolding the inserts 30 as described above. Once the tank material has hardened, the connecting assembly 32 may be located within the interior 20 of the tank such as by being inserted through a hole in the tank wall 18.

-   -   Next, the fuel tank walls 18 may be separated sufficiently to         permit the connecting assembly 32 to be received between the         portions 14, 16 of the tank wall that overlie the inserts 30         —the couplers 62 not being fully received within the tubular         body 64. The couplers 62 may be aligned with the inserts 30.         Then, the fuel tank wall portions may be moved closer together         to push each coupler 62 into the tubular body 64 while also         engaging the heads 42 of the inserts 30 into the body 64 of the         connecting assembly 32, similar to that described above. Once         the coupler first attachment portion 82 is engaged to the insert         heads 42 and the second attachment portion 84 is engaged with         the body 64, the assembly is complete.

While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention. 

The invention claimed is:
 1. A stiffening assembly for a fuel tank having a wall, the assembly comprising: first and second inserts for the wall of a fuel tank, the inserts each comprising a base having flange, a head, and a neck coupling the base to the head, the neck having a portion that is narrower than at least a portion of the head; and an elongate body having first and second couplers at respective first and second ends of the body, each coupler including a pocket sized to receive the head of a respective one of the inserts, wherein the wall of the fuel tank extends continuously between the inserts and the couplers of the elongate body.
 2. The stiffening assembly of claim 1, wherein each insert is integrally formed in one piece.
 3. The stiffening assembly of claim 1, wherein the heads of the inserts each include voids at its distal end.
 4. The stiffening assembly of claim 1, wherein the insert is partially hollow.
 5. The stiffening assembly of claim 4, wherein the insert includes a cavity opening at the base.
 6. The stiffening assembly of claim 5, wherein the inserts include ribs projecting into the cavity.
 7. The stiffening assembly of claim 1, wherein the couplers are separately formed and attached to the elongate body, the couplers and body including corresponding tabs and detents for attachment.
 8. The stiffening assembly of claim 1, wherein the elongate body defines first and second openings at the first and second ends, the first and second openings receiving the first and second couplers.
 9. The stiffening assembly of claim 8, wherein the pockets are defined by a plurality of fingers, the plurality of fingers being moveable between a first state and a second state, the plurality of fingers moving radially inwardly from the first state to the second state, the first and second openings sized to cause the plurality of fingers to move to the second state as the fingers are received within the openings.
 10. The stiffening assembly of claim 1, wherein the elongate body includes two tubular members defining the first and second ends and at least a third end, and further comprising a third insert and a third coupler at the third end.
 11. A fuel tank assembly comprising: a fuel tank having a wall defining a tank interior; and the stiffening assembly of claim 1, wherein a first exterior portion of the wall carries the first insert and a second exterior portion of the wall carries the second insert, and wherein the body and couplers are received within the tank interior.
 12. The fuel tank assembly of claim 1, wherein the head extends from the neck extending from the base of the insert and the wall of the fuel tank is securely trapped between the respective heads of the inserts and the couplers.
 13. A stiffening assembly for a fuel tank having a wall, the assembly comprising: first and second inserts for the wall of a fuel tank, the inserts each comprising a base having flange, a head, and a neck coupling the base to the head, the neck having a portion that is narrower than at least a portion of the head; and an elongate body having first and second couplers at first and second openings defined at respective first and second ends of the body, each coupler including a pocket sized to receive the head of a respective one of the inserts, wherein the pockets are defined by a plurality of fingers, the plurality of fingers being moveable between a first state and a second state, the plurality of fingers moving radially inwardly from the first state to the second state, the first and second openings sized to cause the plurality of fingers to move to the second state as the fingers are received within the openings.
 14. The stiffening assembly of claim 13, wherein each insert is integrally formed in one piece.
 15. The stiffening assembly of claim 13, wherein the heads of the inserts each include voids at its distal end.
 16. The stiffening assembly of claim 13, wherein the insert is partially hollow.
 17. The stiffening assembly of claim 16, wherein the insert includes a cavity opening at the base and further includes ribs projecting into the cavity.
 18. The stiffening assembly of claim 13, wherein the couplers are separately formed and attached to the elongate body, the couplers and body including corresponding tabs and detents for attachment.
 19. The stiffening assembly of claim 13, wherein the elongate body includes two tubular members defining the first and second ends and at least a third end, and further comprising a third insert and a third coupler at the third end.
 20. The stiffening assembly of claim 13, wherein the wall is interposed between the inserts and the couplers. 